Loss of elastic recoil is known to accompany aging and lung destruction (emphysema). This loss is pictured as following: 1) an increase in resting tissue length, 2) a uniform loss of elastic elements (panlobular emphysema), or 3) a localized loss of elastic elements (centrilobular emphysema). These mechanisms may act singly or in concert, but their effect will be evident in measured tissue properties, structure, and the pressure-volume characteristics. Tissue properties of alveolar wall may be estimated by several measures. The pressure-volume characteristics are examined by well known techniques while the morphometry and morphology of the same lung are studied. Maximum extensibility of the tissue before deformation will be compared with such structural changes as mean linear intercept, alveolar and ductal volume proportions, blood barrier thickness, etc. These will be examined in normal and emphysematous lung. From these we may evaluate the relative part played by these different factors from the loss of elastic recoil. In additon, the type and severity of different emphysemas will be compared as to their effect upon elastic recoil.